[TheForge] A different needle question

[Bob]

     I don't have a solution for the heating process but could tempil 
sticks tell you when you have reached the desired temperature?

Bob Willman
The Eagle's Anvil
Bowling Green, Ohio
WB8NQW

To the kindly influence of Christianity we owe that degree of civil
freedom, and political and social happiness, which mankind now
enjoys…Whenever the pillars of Christianity shall be overthrown,
our present republican forms of government – and all blessings
which flow from them – must fall with them.

Jedediah Morse

On 10/21/2013 6:24 PM, Bruce . wrote:
> ​I am altering the eye shape of a few commercial needles.  They're too
> brittle to work without normalizing, but onc​
> ​e normalized, they bend just fine.
>
> Now I need them hard again.  Well, dunking in water while at a red heat
> works for that -- but leaves them more brittle than ever.
>
> A tempering operation (to purple or blue, probably) is quite easy on a
> chisel, but even SEEING the colors on a needle is a challenge.  For one
> thing, there's no good surface to polish.
>
> I've tried a couple methods, all without success -- my toaster over doesn't
> get hot enough, like, maybe 450 F, despite what the dial says.   (520 F =
> purple, 540 F = blue, 590 F = peacock, according to one reference.)  I
> tried heating an iron griddle to these temperatures and leaving the needle
> on it for about 5 minutes -- no luck.
>
> I considered using a salt or solder bath, but find no appropriate salt and
> that I'd need 80/20 to 85/15 lead/tin solder -- which is not readily
> available -- to get a liquid bath of the right temperature.
>
> I'm considering a sand bath or a furnace, using a thermocouple to monitor
> temperature, but as you can see, this is getting increasingly complicated
> for what should be a rather simple task.
>
> Hence, I'm soliciting suggestions how to temper a needle.  Any notions?
>
> Bruce
> NJ
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